1. Field of the Invention
This invention relates to the recovery of petroleum from a subterranean formation and more particularly pertains to recovering heavy viscous petroleum from a formation having low relative permeabilities to oil and water by injecting thermal energy into the formation.
2. Description of Prior Art
There are many processes known in the art for injecting thermal energy into a formation for the purpose of reducing the viscosity of heavy viscous petroleum so that it may be recovered. Such processes are usually classified as "thermal drive," "single well thermal injection" or the like. Thermal drive processes basically involve injecting thermal energy into an oil-bearing formation by means of an injection well, driving the petroleum towards one or more adjacent producing wells and recovering the petroleum through the producing wells. Single well thermal injection processes usually involve injecting thermal energy into the oil-bearing formation by means of an injection well and subsequently withdrawing the resulting heated petroleum through the same well. Such single well thermal injection processes are also commonly referred to as "huff-and-puff" processes. There are, of course, many modified versions of these basic techniques known in the art which employ a wide variety of thermal energy agents, such as hot water, in-situ combustion steam, heated condensable and non-condensable gases, and the like.
Although many thermal injection processes have been useful under certain conditions, there are many formations known to contain large volumes of heavy viscous petroleum from which the petroleum has not been economically and efficiently recovered by the employment of any known thermal injection technique. By way of example, there are many formations located throughout the United States, particularly throughout southern Illinois, western Missouri, southeastern Oklahoma, and southern Kansas, saturated with heavy viscous crudes, e.g., having viscosities greater than 200 centipoises and/or API gravities below about 22.degree. (both at 60.degree. F.), which have not been recovered in economic quantities by employment of conventional "primary" recovery techniques. Additionally, previous attempts to increase the recovery of such heavy crudes from such formations by the employment of known thermal injection processes, especially direct single well steam injection, have been substantially unsuccessful. As known, one of the primary problems in attempting to recover such viscous crudes from such formations is that the formations have such low relative permeabilities to oil and water that thermal energy cannot be injected into the formations at economic injection rates. In fact, there are many formations which have such low relative permeabilities to oil and water that they will not accept sufficient quantities of thermal energy by the employment of known injection processes at any injection rate.
Accordingly, it is a primary object of the present invention to provide a process for economically and efficiently recovering heavy viscous petroleum, e.g., petroleum having a viscosity greater than 200 centipoises and/or an API gravity below about 22.degree. (both at 60.degree. F.) from a formation having low relative permeabilities to oil and water.
It is another object of the present invention to provide a process for heating such low relative permeability formations to permit economic recovery of such highly viscous crudes.
It is a further object of the invention to provide a process for injecting a heated fluid containing steam into a formation saturated with heavy viscous petroleum having such low relative permeabilities to water and oil that it will not accept the injection of the heated fluid containing steam at an economical injection rate by the employment of known thermal energy injection techniques.
It is yet a further object of the invention to provide a process for recovering economic quantities of such highly viscous crudes from such low permeability formations which heretofore have not been economically produced by the employment of known thermal injection processes.